Is there anyone with real hands on experience on this topic?

Kyosho show minimal cut-outs for their .46 sized ARF cowls - carb inlet, glow and external muffler, that's it. OS has confirmed this is OK, yet hobby shops and everyone at the field will tell you to cut your cowl to pieces to allow cooling. Is this just overdoing it though?

Does anyone out there really know the truth, checked engine temps. etc.?

I have just finished a P-51D Mustang and am anxious to know. Failing any info to the contrary, I will follow Kyosho's instructions and see what happens. After all, it is only a small engine. For larger engines sure, I would go with a bigger cut-out because they give off more heat.

As a rule of thumb, C/L stunt guys want to have double the amount of airflow exit area as intake area.

As mentioned, 2x outlet area as inlet area. However, if you tend to put the largest size engine recommended like I normally do, cut a little more out. I had a problem with my World Models Midget Mustang with a OS 91FX leaning out in flight. I would take my cowling off and it would run fine. I decided to cut more of the cowling out and allow air to move throughout the cowling and especially around the engine. It runs fine now.

A buddy of mine made the mistake of not providing enough ventilation with his EZ P-51 with ST 51. He tried to keep it as "pretty" as he could and when it leaned out at low altitude in a bad spot, it went spiraling to the ground.

Thanks for your replies guys, especially the last one. Hmm, so it does lean out and get hot - I will enlarge the cooling holes, although some cowls don't have an "inlet" or do you make one up front underneath and then one at the rear as an outlet?

You can also do as in full size applications, use cylinder head baffles. This will direct the incoming air through the fins rather than around them.

Brass shim stock works well for this. Use two pieces leaving an opening in the front and rear of the cylinder. You can attach with copper wire soldered to the baffles and twisted together then soldered.